1. Field of the Invention
This invention relates to tissue paper webs. More particularly, it relates to soft, absorbent tissue paper webs which can be used in toweling, sanitary tissue, and facial tissue products.
2. Background Art
Paper webs or sheets, sometimes called tissue or paper tissue webs or sheets, find extensive use in modern society. Such items as paper towels, facial tissues, and sanitary (or toilet) tissues are staple items of commerce. It has long been recognized that two important physical attibutes of these products are their softness and their absorbency, particularly their absorbency for aqueous systems. Research and development efforts have been directed to the improvement of either one of these attributes without deleteriously affecting the other as well as to the improvement of both attributes simultaneously.
Softness is the tactile sensation perceived by the consumer as he holds a particular product, rubs it across his skin, or crumples it within his hand. This tactile sensation is a combination of several physical properties. One of the more important physical properties related to softness is generally considered by those skilled in the art to be the stiffness of the sheet of paper from which the product is made.
Absorbency is the measure of the ability of a product, and of the paper tissue webs from which the product may be made, to absorb quantities of liquid, particularly aqueous solutions or dispersions. Overall absorbency as perceived by the human consumer is generally considered to be a combination of the total quantity of liquid a given mass of tissue paper will absorb at saturation as well as the rate at which the mass absorbs the liquid.
Shaw, in U.S. Pat. No. 3,821,068, issued June 28, 1974, teaches that chemical debonders can be used to reduce the stiffness, and thus enhance the softness, of a tissue paper web. Becker et al., in U.S. Pat. No. 4,158,494, issued June 19, 1979, have taught that the strength of a web of tissue paper which has been softened by the addition of chemical debonding agents (which, by their very nature, serve to weaken interfiber bonds within the web) can be enhanced by adhering, during processing, one surface of the web to a creping surface in a fine pattern arrangement by a bonding material, such as an acrylic latex rubber emulsion, a water soluble resin, or another elastermeric bonding material, adhered to one surface of the web and to the creping surface in the fine pattern arrangement, and creping the web from the creping surface to form a sheet material.
Chemical debonding agents have been disclosed in various references such as U.S. Pat. No. 3,554,862, issued to Hervey et al. on Jan. 12, 1971. These materials include quaternary ammonium salts such as trimethylcocoammonium chloride, trimethyloleylammonium chloride, dimethyldi(hydrogenated-tallow)ammonium chloride and trimethylstearylammonium chloride.
The addition of debonding agents to tissue paper webs, while enhancing the softness of the webs, has been shown to decrease the absorbency of the webs. Emanuelsson et al., in U.S. Pat. No. 4,144,122, issued Mar. 13, 1979, who teach the use of complex quaternary ammonium compounds such as bis(alkoxy-(2-hydroxy)propylene) quaternary ammonium chlorides to soften webs, strive to overcome the absorbency decrease problem with the use of nonionic surfactants such as ethylene oxide and propylene oxide adducts of fatty alcohols.
Armak Company, of Chicago, Ill., in their bulletin 76-17 (1977) have taught that the use of dimethyldi(hydrogenated-tallow)ammonium chloride in combination with fatty acid esters of polyoxyethylene glycols may impart both softening and absorbency to tissue paper webs.